Quarter zucchini lengthwise and cut into 6 even pieces (24 total). Cut pepper into 4 even sides, then cut each into 6 pieces (24 total). Peel onion and cut into quarters. Cut each quarter into 6 pieces (24 total). When ready to cook, thread each skewer with 2 chicken pieces, 2 beef pieces, and 3 of each veggie (in any pattern you like). Spread any remaining marinade over veggies.

Preheat a grill or grill pan over medium high heat and coat with cooking spray. Grill skewers for approximately 10 minutes, turning frequently, until chicken is firm and cooked through.